1. Field of the Invention
The present invention relates to a disk cartridge in which a disk used as a recording means used for recording data is rotatably housed and, more particularly, to an improvement in a portion of the disk cartridge which is brought into contact with the center spindle of a drive means which is externally inserted in the disk cartridge so as to rotate the disk.
2. Description of the Related Art
Recently, with the spread of personal computers, personal word processors, and the like, magnetic disk cartridges and the like have been increasingly used as an easy-to-use data recording means.
A 3.5-inch magnetic disk cartridge will be discussed as an example. The magnetic disk cartridge includes a disk coated with a magnetic material as a recording medium, and a pair of upper and lower cases for housing the disk. A hub is arranged at the center of the disk. The hub has holes formed both at its center and a position deviated from the center. Holes are also formed in the corner of the cases. A write protector for inhibiting data recording is positioned in these hole.
A pair of windows are formed in the cases so as to allow a magnetic head for reading from writing data to, the magnetic disk to be inserted. A substantially U-shaped metal shutter is movably arranged to cover part of the cases. A circular hole is formed in one of the cases so as to expose the hub arranged at the center of the disk. Liners made of nonwoven fabrics are respectively formed surfaces of the upper and, lower half cases against the disk so as to remove any foreign substance such as dust. A lifter is arranged between one case and the liner so as to press the liner toward the disk. The substantially U-shaped shutter is fitted on the assembled cases from a side. A spring is engaged with the shutter so as to bias the shutter in one direction.
In the disk cartridge having the above-described arrangement, in order to cause a disk drive means to rotate the disk, the center spindle is inserted into the center hole of the hub. In order to ensure a space in the cartridge, the center spindle is always brought into contact with the inner surface of the case which opposes the center spindle. For this reason, when the center spindle is rotated, the inner surface of the case is abraded by the spindle. As a result, dust is generated from the case upon abrasion, and a read error may be caused.
Published Unexamined Japanese Utility Model Application No. 62-69870 discloses a means for eliminating this drawback. According to the magnetic disk cartridge disclosed in this application, a lubricating polymer sheet is arranged, as a center sheet, on the inner surface of the case with which the center spindle is brought into contact. The center sheet consists of a resin such as ultra-high-molecular polyethylene. With this center sheet, scraping is not readily caused upon rotation of the center spindle, and hence dust is not easily generated, thus reducing the frequency of errors due to dust and the like.
Recently, higher recording capacities of such a recording apparatus and recording material have been achieved. This tendency is also recognized in the above-described type of magnetic disk cartridges. For this purpose, the recording tracks of the magnetic disk are narrowed, and the intervals of the tracks are reduced, and linear recording density is increased. Along with this tendency, in order to shorten the access time, the read speed of the recording tracks must be increased. For this purpose, the magnetic disk must be rotated at or even higher speed.
If the magnetic disk is rotated at a higher speed, substantial abrasion occurs even with a center sheet consisting of a generally used material. It was discovered through experimentation that hard materials, such as a lubricant-infiltrated sintered metal and surface is fluorinated, metals as the hard materials don't have a resilience, abrasion becomes more conspicuous than with center sheets consisting of the conventional materials. In addition, since the magnetic disk which is rotated at high speed inevitably has narrowed recording tracks and reduced track intervals, the adverse influences of dust are greatly increased. That is, even dust of a size which does not cause an error in normal tracks may cause an error in high-density narrow tracks. Therefore, reduction in foreign substance such as dust generated in a disk cartridge becomes indispensable for a magnetic disk with an increased data recording capacity.